Streptococcus sanguis plays a central role in dental plaque formation because of its high affinity for salivary pellicle and its ability to interact with other organisms. An adhesin, designated the A antigen, has been shown to be directly correlated with the attachment of S. sanguis G9B to saliva coated hydroxyapatite (SHA) which is an accepted model for the salivary pellicle. The adhesin is a protein or possibly a glycoprotein and is composed of three polypeptides whose molecular weights are 80, 62 and 52 kDa (the 80 kDa antigen complex). Antibody against the A antigen or the native 80 kDa inhibits attachment of G9B to SHA. Although antibody to the denatured 80 kDa protein reacts with the 80 kDa antigen complex, it does not react with the A antigen nor does it inhibit attachment. These properties suggest that adhesion to SHA is associated with conformational rather than sequential epitopes. Regulation of adhesin activity may be associated with an adhesin protease which was also found in S. sanguis. The objectives of the proposed studies are to determine the function domains of the adhesin and the role of the adhesin protease in governing the ability of S. sanguis strains to attach to salivary pellicle. The studies will utilize a combination of biochemical, immunological and molecular biological approaches to characterize the functional domains of the adhesin molecules. In order to accomplish the latter goal a genomic library of the chromosome of G9B has been constructed in Escherichia coli using an EMBL3 vector. The biological role of the protease in regulating ecological interactions will be explored by creating a protease deficient mutant of G9B by insertional inactivation of the protease gene isolated from this library. Control of dental plaque formation has become a central tenet in new approaches to the reduction of dental caries and periodontal disease. It has become clear that shotgun approaches to controlling plaque formation often results in unwanted side effects and therefore attention has been focused on mechanisms of specifically controlling this process. An understanding of the mechanisms of interaction between the bacterial surface polymers and the salivary proteins involved is the first step in developing biological and chemotherapeutic agents for regulating initial events in dental plaque formation.